DESCRIPTION (Applicant's Abstract): The intermediate withdrawal phase following high-dose cocaine binges (3-14 days after stimulant withdrawal) is associated with a high rate of recidivism. Thus, understanding neurobiological alterations during this period may be critical in formulating a rational treatment mode against repeated high-dose stimulant abuse. To this end, the main focus of our project is a development of an animal model for the intermediate withdrawal phase with an emphasis on presynaptic regulation of dopamine neurotransmission. We have proposed that continuous cocaine pretreatment via osmotic minipumps, which leads to a behavioral tolerance during withdrawal, might be an animal model of compulsive abuse in humans. Time-dependent alterations in the presynaptic DA mechanisms following this regimen will be directly compared and contrasted to those following an intermittent injection regimen, a model of early stages of cocaine abuse characterized by a sensitization. After 1 and/or 7 days after withdrawal, we will (1) continue characterization of the time-dependent changes in the sensitivity of soma/dendritic and terminal autoreceptors regulating dopamine impulse-flow and release, respectively; (2) determine the number of active dopamine neurons and their bursting pattern and possible role of dopamine D1 and D2 receptors in mediating these changes; (3) characterize the role of local D1 receptors in the substantia nigra in mediating the altered sensitivity of dopamine neurons to mixed direct agonists; and (4) characterize changes in the regulation of terminal uptake in the prefrontal cortex (as well as caudate and nucleus accumbens) using a fast scan cyclic voltammetry. We will utilize in vivo microiontophoretic application of dopamine agonists and antagonists and in vitro photolytic application of "caged-dopamine" for assessing autoreceptor changes. We will also use a standard neuronal population sampling methodology ("9-track"). The "caged-dopamine" in combination with the voltammetric technique will be used to assess altered baseline dopamine release/uptake and its modulation in the dopamine terminal areas. By carefully examining time-dependent changes in the presynaptic dopamine regulation, this project is expected to aid in identification of important mechanisms, which might be associated with the intermediate withdrawal phase and, thus, would be amenable to pharmacotherapeutic intervention.